1. Field of the Invention
This invention relates generally to rubber compositions and designs for improved snap-in tire valves, more particularly to snap-in valves having a metal-adhesive, heat-resistant EPM rubber composition, and specifically to a snap-in tire valve having two rubber layers, one with the metal adhesive composition and one with non-metal-adhesive rubber.
2. Description of the Prior Art
Tire valves of the snap-in type are known. A shaped resilient seal is commonly over molded around a brass valve body. The seal shape generally includes a circumferential ridge or rib that must be compressed or otherwise deformed to let the seal snap into the valve hole in the wheel rim and a groove that retains the valve in the valve hole. The resilient seal then supports the valve body and seals the hole. The support and sealing functions are expected to last the life of the tire. U.S. Pat. Nos. 3,287,485 and 3,670,688 disclose examples of valves of rubber and brass that snap into a wheel rim. The '485 patent discloses a suitable styrene-butadiene rubber (SBR) formulation and a suitable butyl rubber (BR) formulation for the rubber seal. The '688 patent discloses that adhesives may be used to bond the rubber to the valve body. Sulfur-cured ethylene propylene diene elastomer (“EPDM”) and natural rubber have also been used for the rubber component.
Tire pressure monitoring system (“TPMS”) applications generally include a pressure sensing module mounted on the valve body inside the wheel. U.S. Pat. Nos. 6,005,480 and 7,281,421 disclose tire pressure sensor assemblies including a tire valve that can snap into a wheel rim. The added mass of the sensor results in much higher demands placed on the rubber seal of the valve. These demands are further aggravated by high speeds of revolution, high accelerations, and by wheels that are reportedly running hotter than in the past which may be due to heat transferred to wheel rims from brake systems. Thus, applications of TPMS can experience accelerations of up to 1400 Gs and operating temperatures of up to 100° C. These demands have caused conventional snap-in tire valves to fail early due to cracks at various critical locations in the rubber seal, adhesion loss, and/or other problems due to thermal or heat aging of the rubber.
Snap-in tire valves are to be distinguished from other designs, such as bolt-on designs, rigid designs, and the like, which use entirely different sealing methods, such as o-rings, gaskets, permanent welds, or the like.